This invention relates to a negative pressure air bearing (NPAB) head slider for use in, in particular, a disk drive incorporating a head disk assembly of a ramp loading type, said head slider has a read/write element for recording and reproducing data onto and from a disk as a recording medium.
In the field of hard disk drives (HDD), the reduction of the flying height of head sliders is demanded in accordance with the development of recording density enhancing techniques. In HDDs, the slider in a flying state moves over the rotating disk when performing an access operation. In a target position on the disk, the data read/write operation is performed by a read/write element (which is also called a "magnetic transducer") mounted on the slider. The aforementioned flying height indicates spacing between the disk surface and the read/write element. The lower the flying height of the slider, the greater the recording/reproducing characteristics of the head.
In a head disk assembly of a contact start stop (CSS) type employed in conventional HDDs, the slider is kept in contact with a CSS area provided on the disk (usually, the radially innermost portion of the disk) when the drive is stopped. To prevent the slider from being adhered to the disk because of static friction and adhesion forces, the disk surface is made rough. This rough surface, however, limits the reduction of the flying height since the slider will collide with bumps of the rough surface if the flying height is too low.
In light of the above, attention is now paid to a ramp loading type head disk assembly, in which the slider and the disk are kept out of contact when the drive is stopped. The ramp loading type is also called a "dynamic head loading and unloading type". Since the ramp loading type permits the slider and the disk to be kept out of contact with each other, the adhesion problem can be avoided. Accordingly, it is not necessary to make the disk surface rough, and hence further reduction of the flying height of the slider can be realized.
Moreover, it is important to stabilize the slider, as well as reduct its flying height. To this end, suppression of fluctuations in the slider's flying height is demanded, which are caused by internal factors such as manufacturing tolerances of component parts of the drive, and by external factors such as pressure fluctuations. A negative pressure air bearing (NPAB) slider is effective to satisfy the demand.
The NPAB slider uses negative air pressure that is applied to the disk (in a direction opposite to positive air pressure that is applied to the slider to raise it from the disk surface). In HDDs, the slider is held by a suspension attached to the actuator arm, and is urged by the suspension toward the disk. Fluctuations of the flying height are suppressed by balancing the sum of the suspension load and the negative air pressure with the positive air pressure applied to the slider, thereby enhancing the rigidity of the air bearing.
In general, an NPAB slider 3 (hereinafter referred to just as a "slider") is held by a suspension 2 via gimbals 2B as shown in FIG. 12A. In this state, a suspension load (Fs) is applied from a pivot 2A provided on the suspension 2 toward the surface of a disk 1. In other words, the slider 3 is urged toward the disk surface. Since the disk 1 is rotated at high speed (in a direction indicated by arrow 100), the slider 3 has an air inlet side (300A) and an air outlet side (300B) with respect to the disk surface, as is shown in FIG. 12B.
A positive pressure (Fp) is applied to the slider 3 as a result of air flowing into a positive pressure generating (PPG) section (30, 32) thereof located close to the disk. The positive pressure (Fp) raises the slider 3 from the disk surface. On the other hand, a negative pressure (Fn) is applied to the slider 3 from a negative pressure generating (NPG) section 31. The negative pressure (Fn) urges the slider 3 toward the disk surface. FIG. 12B shows the suspension load (Fs), the positive pressure (Fp), the negative pressure (Fn), and points (Ps, Pp, Pn) at which the load and forces are exerted, respectively.
The PPG section of the slider 3 comprises a horse shoe-shaped bottom surface 30 (which can be brought into contact with the disk surface), and a relatively shallow step section 32 with respect to the bottom surface 30. The NPG section 31 of the slider 3 is a relatively deep step section with respect to the bottom surface 30. A read/write element 3A is provided at an outlet-side end of the bottom surface 30. At the time of unloading, when the slider 3 is separated from the disk 1, the positive pressure (Fp) is exerted in a narrow space (Fha) defined between the bottom surface 30 and the surface of the disk 1, while the negative pressure (Fn) is exerted in a space (FHb) defined between the deep stepped section 31 and the surface of the disk 1.
At the beginning of unloading, the positive pressure (Fp) applied to the slider 3 relatively quickly reduces, whereas the negative pressure (Fn) does not so abruptly reduce. At this time, in which the negative pressure (Fn) is relatively large, an unloading force (Fu) is generated in a middle stage of unloading as shown in FIG. 13, whereby a stage in which the slider 3 sucks to the disk surface occurs. This stage occurs when a back surface of the slider 3 is separated from the pivot 2A by the relatively large negative pressure (Fn) to thereby deform the gimbals 2B.
To hold the slider 3 by a ramp member 10 so as to completely unload it from the disk 1 after the transitional stage, it is necessary to raise the slider 3 to a sufficiently high level. The ramp load mechanism used for raising the slider 3 high is a factor that impedes the thinner construction of the drive mechanism. Further, where the negative pressure (Fn) and the unloading force (Fu) balance with each other, the rigidity of the air bearing is low, which will make the flying state of the slider 3 unstable. Accordingly, when the slider 3 is unloaded from the disk 1, it is very possible that they will contact each other, which may lead to their breakage.
Referring to FIGS. 10 and 11, the problem of reduction of the slider's flying height at the time of unloading will be described. When in the ramp loading type HDDs, the supply of power has been erroneously interrupted, it is necessary to unload the slider 3 before the rotation of the disk 1 stops. In other words, a high-speed unloading operation is required. FIG. 10 is a view useful in explaining relative movement of the slider 3 and the disk 1 at the time of unloading. The yaw angle 70 of the slider 3 with respect to the disk 1 (which rotates in a direction indicated by arrow 100) gradually varies from the inner edge to the outer edge of the disk 1, when using a rotary head actuator. In the case of a usual drive, the yaw angle 70 of the slider 3 is designed such that it is smaller at the inner edge side and larger at the outer edge side.
FIG. 11 shows the relationship between the yaw angle of the slider 3 (abscissa) and the flying height (ordinate: FH). As shown in FIG. 12B, the usual slider 3 has a horse shoe-shaped bottom 30 including two leg portions substantially extending in the direction of rotation of the disk 1. The positive pressure (Fp) generated by the slider 3 of this structure reduces when the yaw angle increases. Accordingly, the flying height (FH) of the slider 3 shows a tendency to reduce as the yaw angle increases, as is indicated by curve 80 in FIG. 11. Since, in the usual drive, the rotational speed of the disk is constant, the slider's flying height shows a tendency to increase as the circumferential speed increases from the inner edge side of the disk 1 to the outer edge side. On the other hand, since the yaw angle of the slider 3 is larger at the outer edge side of the disk 1, the slider's flying height shows a tendency to reduce at the outer edge side. These tendencies offset each other to thereby realize a relatively uniform flying height pattern of the slider 3 from the inner edge side to the outer edge side of the disk 1.
As is shown in FIG. 10, the relative movement of the slider 3 and the disk 1 at the time of unloading is expressed by the vector sum (indicated by arrow 73) of the circumferential speed of the disk (indicated by arrow 72) and the unloading speed of the slider 3 (indicated by arrow 74), with the result that the yaw angle increases by an angle indicated by arrow 71. The increase of the yaw angle causes a significant reduction (as indicated by reference numeral 82 in FIG. 11) in the slider's flying height. This reduction of flying height will cause the disk 1 and the slider 3 to contact each other, and hence may cause their breakage.
As described above, in HDDs in which a ramp loading (dynamic head loading and unloading) head assembly is combined with an NPAB slider, the flying state of the slider is unstable, and at worst, the slider may contact the disk and adhere to it. An NPAB slider sucks to the disk during unloading. To prevent such suction, it is necessary to increase the height of the ramp member. Increasing the height, however, impedes the thinner construction of the disk drive. Further, another type of an NPAB slider is proposed which has a structure as shown in FIGS. 14A and 14B. In this case, the NPG section 31 greatly protrudes into the air inlet side (300A) so as to enable the generation of as high a negative pressure (Fn) as possible in a limited area. As a result, the point (Pn) of application of the negative pressure (Fn) is situated at the inlet side (300A), while the point (Pp) of application of the positive pressure (Fp) and the point (Ps) of application (i.e. the pivot position) of the suspension load (Fs) are situated at the outlet side (300B). Even when in this structure, the suspension load (Fs) reduces at the time of unloading, the amount of pitching of the slider 3 (indicated by reference letters PT in FIG. 14A) does not increase, and a change in space between the inlet-side (300A) end of the PPG section 32 and the disk surface is small. Accordingly, as mentioned above, the slider 3 will suck to the disk 1 because of the negative pressure (Fn), which means that the flying state of the slider 3 becomes unstable and may contact the disk 1 when it is unloaded.